Total knee prosthesis and range of elements for producing said prosthesis

ABSTRACT

The invention concerns a prosthesis ( 1 ) comprising a femoral implant ( 2 ) and a tibial implant ( 3 ) equipped with anchoring rods ( 21 ), each anchoring rod ( 21 ) not being integral with the corresponding implant and capable of being connected thereto, the prosthesis ( 1 ) including therefor means ( 16, 20; 36, 34 ) for assembling each anchoring rod ( 21 ) to the corresponding implant ( 2, 3 ). The invention is characterized in that the means ( 16, 20; 36, 34 ) for assembling each medullar anchoring rod ( 21 ) to the corresponding implant ( 2, 3 ) are configured to allow a plurality of possible angular positions of that same anchoring rod ( 21 ) relative to the implant ( 2, 3 ) in translation along an axis inscribed in the frontal plane, that is lateral, or in the sagittal plane, that is antero-posterior, of the implant.

The present invention relates to a total knee prosthesis and a series ofcomponents enabling composition of this prosthesis.

In certain cases, arthroplasties of the knee are particularly difficultto achieve, the ligaments of the joint being faulty, even inoperative,and/or the quality of bone epiphyses being insufficient to enable astable support of the femoral implant and of the tibial implant.

Among the existing knee prostheses, certain ones, called “joint”,comprise a bicondylar femoral implant, a femoral implant mechanicallyconnected to the tibial implant and pivotably guided relative to itabout a determined transverse axis, and an intermediate fixed plateaumade of polyethylene.

These prostheses have the disadvantages of not being modular and notenabling restoration of a mechanically stable joint with a favorabledistribution of loads. Instead, these prostheses induce significantstresses at the joint surfaces and bone anchors.

Another type of “joint” prosthesis comprises a tibial implant equippedwith a longitudinal stud on which is fitted a tubular componentconnected to the femoral implant, this fitting enabling stabilization ofthe femur and the tibia in the sagittal plane and thus making up for thedeficiencies of the ligaments. The implants of these prostheses areequipped with fixed anchoring rods, which have a disadvantage ofgenerating significant stresses localized on the longitudinal stud andon the bone anchors. It results in risks of premature wear of theprosthesis and risks of loosening of the implants.

Yet another type of “joint” prostheses, more developed, comprises apolyethylene plateau designed to distribute stresses on the twoplateau/femoral implant and plateau/tibial implant interfaces. However,the significant possibility of rotation of the tibial plateau induces aninstability of the prosthesis when the lower member is extended.

Document U.S. Pat. No. 5,879,391 describes a knee prosthesis withfemoral and tibial anchoring rods adjustable in position. The femoralanchoring rod is adjustable in translation in the sagittal plane (FIGS.1 to 6) and the tibial anchoring rod is adjustable in translation in thefrontal plane (FIGS. 7 to 10).

Document U.S. Pat. No. 5,236,359 describes a bone implant comprising atransverse slide 15 in a dovetail, a base 2 slidably engaged in thisslide and an anchoring rod connected to the base. The slide can belongitudinal.

The adjustments in position contemplated by these documents do notenable effective remedy of the aforesaid risks of premature wear of theprosthesis and loosening of the implants.

The present invention aims to solve this problem is, generally, forremedy of the drawbacks of existing prostheses.

Its principal objective is to enable the reconstruction of a knee jointby means of a prosthesis fully adaptable to the specific anatomy of thejoint to be treated and thus having a reduced risk of wear andloosening.

Another objective of the invention is to provide such a prosthesis,adapted to a difficult arthroplasty, that is to say when the jointligaments are deficient, even inoperable, and/or when the joint hasepiphyseal deformities or bone gaps caused by trauma or previoussurgeries.

An additional objective of the invention is to provide such aprosthesis, having a high stability when the lower member is extended.

An additional objective of the invention is to provide a series ofmodular components enabling composition of a prosthesis fully adapted tothe specific anatomy of the joint to be treated.

The prosthesis concerned comprises, in a manner known per se, a femoralimplant and a tibial implant equipped with medullar anchoring rods andan intermediate plateau made of material promoting sliding, inparticular, made of high density polyethylene, each medullar anchoringrod of an implant is not integral with this implant and is connectableto it, the prosthesis comprising to this end means for the coupling ofeach medullar anchoring rod to the corresponding implant and tighteningmeans to immobilize each medullar anchoring rod relative to thecorresponding implant.

According to the invention, the means that the prosthesis comprises forthe coupling of each medullar anchoring rod to the corresponding implantare designed to enable a plurality of possible angular positions of themedullar anchoring rod relative to the implant and a plurality ofpossible positions of this same medullar anchoring rod relative to theimplant in translation along an axis contained in the frontal plane,that is to say lateral, or in the sagittal plane, that is to sayanteroposterior, of the implant.

Due to this double adjustability of the position of a medullar anchoringrod relative to the corresponding implant, it is possible to accuratelyposition the anchoring rods relative to the femoral and tibial implantsaccording to the specific anatomy of the patient and thus obtain anoptimal functioning of the prosthesis regardless of this anatomy. Theprosthesis consequently has greatly reduced risks of wear and loosening.

Preferably, the means for the coupling of the femoral anchoring rod tothe femoral implant are designed to enable angular adjustment of theanchoring rod in the frontal plane and the adjustment in translation ofthis rod in the sagittal plane.

Preferably, the means for the coupling of the tibial anchoring rod tothe tibial implant are designed to enable angular adjustment of theanchoring rod in the sagittal plane and the adjustment in translation ofthis rod in the frontal plane.

According to a preferred from of implementation of the invention,

-   -   at least one anchoring rod is designed to be connected to the        corresponding implant by an intermediate coupling part;    -   this intermediate coupling part has means for the coupling of        the rod to it and a curved end wall;    -   the implant has a cavity for reception and retention of the        aforementioned curved end wall, having the same profile as the        aforementioned curved end wall and the bottom of which is        delimited by a curved reception wall against which comes to bear        the aforementioned curved end wall at the time of the coupling;        this curved reception wall has an arc length greater than that        of the aforementioned curved end wall, so that this curved end        wall, and thus the aforementioned anchoring rod connected to it,        can be positioned according to several angular positions        relative to the implant; the cavity is shaped along an axis        contained in the frontal plane or in the sagittal plane of the        implant so that it enables the sliding of the aforementioned        curved end wall in it in order to carry out the adjustment in        translation of the medullar anchoring rod relative to the        implant.

Advantageously, the means for the coupling of a medullar anchoring rodto an intermediate coupling part comprise:

-   -   a threaded bore longitudinally traversing the intermediate        anchoring part and opening into the concave face of the        aforementioned curved end wall;    -   a threaded rod integral with the medullar anchoring rod, adapted        to be screwed into the aforementioned threaded bore, this rod        having a length slightly greater than that of the bore so as, in        coupling position of the medullar anchoring rod to the        intermediate coupling part, to bear against the aforementioned        curved reception wall and thus tighten the intermediate coupling        part against the walls of the implant delimiting the        aforementioned cavity for reception and retention of the        aforementioned curved end wall.

This bore, this threaded rod and these walls of the implant thus alsoforming the aforesaid tightening means enabling immobilization of amedullar anchoring rod relative to the corresponding implant.

In practice, consequently, the medullar anchoring rod is connected byscrewing to the intermediate coupling part without complete tightening,then the position of the medullar anchoring rod is adjusted; thecomplete tightening of the medullar anchoring rod relative to theintermediate coupling part is then carried out to immobilize this rodand this part relative to the implant.

The prosthesis according to the invention can, in particular, be aprosthesis with limited movement of the femoral implant relative to thetibial implant in translation in the sagittal plane, such as aprosthesis called “posterior-stabilized”, that is to say comprisingstops for limiting the aforementioned translation, or a prosthesiscalled “joint”, that is to say comprising means for mounting of thefemoral implant relative to the tibial implant reducing the possibilityof movement of the femoral implant relative to the tibial implant with apivoting according to a determined transverse axis.

The aforesaid double adjustability enables the use of such implants withrestricted movement of the femur, without exercise of significantstrains on the joint areas from the femoral implant to the tibialimplant or on the bone anchor areas.

The prosthesis according to the invention can be a prosthesis with twocondyles; preferably, it is a prosthesis with three condyles, that is tosay having, at the femoral implant and the intermediate plateau, curvedsupport surfaces arranged at the middle, between the two lateralcondyles.

The intermediate plateau can be fixed on the tibial implant, or may bemovable relative thereto. Preferably, in this second case, that meansare provided to limit the pivoting of the intermediate plateau relativeto the tibial implant, in particular, a stud protruding from the plateauthat forms the tibial implant and a groove in a circular arc centered onthe pivot axis of the intermediate plate, arranged in this intermediateplate, this groove receiving the aforementioned stud and cooperatingwith it to limit the pivoting of the intermediate plateau relative tothe tibial implant.

Advantageously, the femoral implant and/or tibial implant comprise meansfor mounting on them one or several shims or spacers enablingcompensation for possible bone ablations or absences at the supportsurfaces of the implants against the femur and/or tibia.

The series of components of the invention comprises:

-   -   at least one femoral implant, at least one tibial implant and at        least one intermediate plate, and preferably the femoral and        tibial components of different sizes having connecting means for        the medullar anchoring rods of identical dimensions and shapes        of one component to the other;    -   at least two intermediate coupling parts;    -   at least two medullar anchoring rods, and preferably more than        two medullar rods anchor, having different diameters, lengths,        shapes and, these medullar anchoring rods being assembled to the        aforementioned intermediate coupling parts

The modularity of these components enables implementation of aprosthesis fully adapted to the specific anatomy of the joint to betreated.

The aforementioned series can also comprise shims or spacers forcompensation of bone ablations or absences, having differentthicknesses, adapted to the reconstruction of adequate support surfacesfor the femoral and tibial implants.

The invention will be well understood, and other features and advantagesthereof will become apparent, with reference to the attached schematicdrawing, representing, as non-limiting example, a preferredimplementation of the prosthesis to which it relates.

FIG. 1 is a perspective view, before assembly;

FIG. 2 is a perspective view, before assembly, from another angle,

FIG. 3 is a perspective view, under assembly;

FIGS. 4 and 5 are perspective views of two intermediate coupling partsthat comprise the prosthesis;

FIG. 6 is a median sectional view in the sagittal plane of theprosthesis after assembly, and

FIG. 7 is a sectional view along the line VII-VII in FIG. 6, in thefrontal plane, of the prosthesis.

The figures show a total knee prosthesis 1, comprising, as is wellknown, a femoral implant 2, a tibial implant 3 and an intermediateplateau 4.

The femoral implant 2 has an enveloping “shield” shape, defining on itsexterior face two lateral condyles 5 and a prosthetic trochlea 6 and, onits interior face, facets 8 for support against the end of the dulyresected bone. In the example shown, the femoral implant 2 also has acentral condyle 9, enabling increase of the surface for support of thefemoral implant 2 against the intermediate plateau 4. It also comprisestapped blind holes 10, opening at distal and posterior facets 8, formounting of one or several shims or spacers (not shown), which enablecompensation for possible bone ablations or absences at the surfaces forsupport of the implant 2 against the femur.

The prosthesis 1 is of the type called “joint” in which the femoralimplant 2 is mechanically connected to the tibial implant 3 and isguided by pivoting relative to the latter about a transverse axisdetermined in order to make up for the deficiencies of the ligaments ofthe joint of the patient. To this end, the femoral implant 2 comprises arear socket 11 pivotally mounted relative to it by means of pivots 12engaged in bearings, these bearings being arranged in two longitudinalbulkheads 13 that form the femoral implant 2 on its interior face. Thesocket 11 is axially drilled and receives a packing 14 made of amaterial promoting sliding, in particular made of high densitypolyethylene.

As FIGS. 3, 6 and 7 show it more particularly, the femoral implant 2forms, in front of walls 13, a solid block 15 in which is fitted in agroove 16 opening at the proximal face and at the posterior face of theblock 15. This groove 16 is shaped according to an axis contained in thesagittal plane of the implant 2 and has a circular arc shape in itslower part and a rectangular shape in its upper part, the upper partbeing narrower than the lower part.

The groove 16 is designed to receive an intermediate coupling part 20 ofthe medullar anchoring rod 21 of the femoral implant 2 to the femur.

The part 20 is more particularly visible in FIG. 4. It comprises acurved end wall 20 a, made in a circular arc, having an arc length lessthan that of the wall delimiting the bottom of the groove 16, a proximalboss 20 b, whose base has a width less than that of the upper part ofthe groove 16, and a bore 20 c arranged along the axis of the boss 20 b,piercing the part 20 from side to side and tapped at the base of theboss 20 b and at the wall 20 a.

The wall 20 a and the boss 20 b are designed to be respectively engagedin these upper and lower parts of the groove 16, with the possibility ofsliding in the sagittal plane, as shown in dotted lines in FIG. 6, andwith the possibility of pivoting in the frontal plane, as shown indotted lines in FIG. 7.

As for the medullar anchoring rod 21, it has a distal portion 21 adesigned to be engaged in the bore 20 c, threaded at its end and havinga length slightly greater than that of the bore 20 c. As can beunderstood in reference to FIGS. 6 and 7, the rod 21-part 20 assemblycan slide and pivot in the groove 16 before complete tightening of therod 21 relative to the part 20, and is locked in position after completetightening of this rod 21 relative to the part 20, the distal portion 21a coming to bear in this position against the rounded boss delimitingthe bottom of the groove 16 and consequently tightening the curved wall20 a against the edges of the block 15 delimiting the upper part of thisgroove. It is thus possible to adjust the position of the medullar rod21 relative to the femoral implant 2 by anteroposterior sliding and bytilting in the frontal plane and then immobilizing this rod 21 in theselected position.

For its tightening, the rod 21 has two flat sections 25 enabling theengagement of a suitable tightening tool.

The tibial implant 3 forms a plateau 30 designed to recreate the upperplateau of the tibia. On its proximal face, this plateau 30 has aposterior stud 31 designed to be received, in an adjustable manner, inthe packing 14 of the socket 11 and an anterior stud 32 designed tocooperate with a groove 43 of the intermediate plateau 4. On its distalface, the plateau 30 has a block 35 integral with it, in which isarranged a groove 36 and lateral walls 37 for reinforcement and settingrelative to the bone. The groove 36 extends in a medial direction and isshaped, and has a shape similar to that of the groove 16.

As FIGS. 2 and 6 show it more particularly, the tibial implant 3receives a medullar anchoring rod 21 identical to the medullar anchoringrod 21 of the femoral implant 2, by means of an intermediate couplingpart 34 similar to the part 20. As it is shown more particularly in FIG.5, this part 34 comprises a curved wall 34 a, a conical boss 34 b and apartially threaded bore 34 c. This part 34 and the groove 36 enable anadjustment of the position of the rod 21 in inclination in the sagittalplane, as it is shown in FIG. 6 in dotted lines, and in sliding in themedial direction, as it is shown in FIG. 7 in dotted lines.

The figures also show that the plateau 30 can receive against it lowerface a shim or spacer 38 enabling compensation for possible boneablations or absences at the support surfaces of the implant 3 againstthe tibia. This shim or spacer 38 comprises an opening 39 having a shapeadapted to its engagement around the block 35 and the walls 37, as FIG.2 shows it.

The intermediate plateau 4 is made of a slide promoting material, inparticular made of a high density polyethylene. It comprises two glenoidside cavities 40 for reception of the lateral condyles 5, an anteriormedian eminence 41 designed to cooperate with the central condyle 9 ofthe femoral implant 2, a posterior bore 42 for reception of the socket11 and the aforementioned groove 43 designed to cooperate with theanterior stud 32. The bore 42 enables a pivoting of the femoral implant2-intermediate plateau 4 assembly about the axis of the stud 31, and theslot 43, centered on the axis of the bore 42, cooperates with the stud32 to limit this pivoting to a sector delimited by the future positionsof the stud 32 in abutment against the ends of this groove 43.

In practice, the medullar rods 21 are connected by screwing to therespective intermediate coupling parts 20, 34 without completetightening then the suitable positions of the rods 21 are adjusted; thecomplete tightening of the rods 21 relative to the parts 20 and 34 isthen carried out to immobilize these rods and these parts relative tothe implants 2, 3.

As it appears from the foregoing, the invention provides a prosthesishaving the decisive advantages of being fully adaptable to the specificanatomy of the joint to be treated, of thus having a reduced risk ofwear and loosening, of being capable of being adaptable to a difficultarthroplasty, and having a high stability when the lower limb isextended.

It is evident that the invention is not limited to the form ofimplementation described above by way of example but it extends to allforms of implementation covered by the attached claims. It is thus thatthe term “medullar anchoring rod” must be understood in a broad sense,including short rods similar to “studs”, the plurality of angularpositions of a medullar anchoring rod could be obtained by means of aball joint type; the plurality of positions in translation could beobtained by sliding of a slide on a rail or in a slide.

1. A total knee prosthesis, comprising a femoral implant and a tibialimplant equipped with medullar anchoring rods, and an intermediateplateau made of a material promoting sliding, in particular, comprisinghigh density polyethylene, each medullar anchoring rod of an implant isnot integral with the implant and is connectable to it, the prosthesiscomprising to this end means for the coupling of each medullar anchoringrod to the corresponding implant and tightening means for immobilizingeach medullar anchoring rod relative to the corresponding implant; theprosthesis characterized in that the means that it comprises for thecoupling of each medullar anchoring rod to the corresponding implant aredesigned to enable a plurality of possible angular positions of themedullar anchoring rod relative to the implant and a plurality ofpossible positions of this same medullar anchoring rod relative to theimplant in translation along an axis contained in the frontal plane,that is to say lateral, or in the sagittal plane, that is to say,anteroposterior, of the implant.
 2. A prosthesis according to claim 1,characterized in that the means for coupling of the femoral anchoringrod of the femoral implant are designed to enable angular adjustment ofthe anchoring rod in the frontal plane and the adjustment in translationof this rod in the sagittal plane.
 3. A prosthesis according to claim 1,characterized in that the means for the coupling of the tibial anchoringrod to the tibial implant are designed to enable angular adjustment ofthe anchoring rod in the sagittal plane and the adjustment intranslation of this rod in the frontal plane.
 4. A prosthesis accordingto claim 1, characterized in that: an anchoring rod is designed to beconnected to the corresponding implant by an intermediate coupling part;this intermediate coupling part has means for the coupling of the rod toit and a curved end wall; the implant has a cavity for reception andretention of the aforementioned curved end wall, having the same profileas the aforementioned curved end wall and the bottom of which isdelimited by a curved reception wall against which comes to bear theaforementioned curved end wall at the time of the coupling; this curvedreception wall has an arc length greater than that of the aforementionedcurved end wall, so that this curved end wall, and thus theaforementioned anchoring rod connected to it, can be positionedaccording to several angular positions relative to the implant; thecavity is shaped along an axis contained in the frontal plane or in thesagittal plane of the implant so that it enables the sliding of theaforementioned curved end wall in it in order to carry out theadjustment in translation of the medullar anchoring rod relative to theimplant.
 5. A prosthesis according to claim 4, characterized in that themeans for the coupling of a medullar anchoring rod to an intermediarycoupling part comprise: a threaded bore longitudinally traversing theanchoring part and opening into the concave face of the aforementionedcurved end wall; a threaded rod integral with the medullar anchoringrod, adapted to be screwed into the aforementioned threaded bore, thisrod having a length slightly greater than that of the bore so as, incoupling position of the medullar anchoring rod to the intermediatecoupling part, to bear against the aforementioned curved reception walland thus tighten the intermediate coupling part against the walls of theimplant delimiting the aforementioned cavity for reception and retentionof the aforementioned curved end wall.
 6. A prosthesis according toclaim 1, characterized in that it is a prosthesis having limitedmovement of the femoral implant relative to the tibial implant intranslation in the sagittal plane, such as a prosthesis called“posterior-stabilized”, that is to say, comprising stops for limitingthe aforementioned translation, or a prosthesis called “joint”, that isto say comprising means for mounting of the femoral implant relative tothe tibial implant reducing the possibility of movement of the femoralimplant relative to the tibial implant with a pivoting according to adetermined transverse axis.
 7. A prosthesis according to claim 1,characterized in that it comprises three condyles, that is to say thatit has, at the femoral implant and at the intermediate plateau, curvedmedian surfaces support arranged between the lateral condyles.
 8. Aprosthesis according to claim 1, characterized in that the intermediateplateau is movable relative to the tibial implant.
 9. A prosthesisaccording to claim 8, characterized in that means are provided to limitthe pivoting of the intermediate plateau relative to the tibial implant,in particular, a stud protruding from the plateau that forms the tibialimplant and a groove in a circular arc centered on the pivot axis of theintermediate plateau, arranged in this intermediate plateau, this groovereceiving the aforementioned stud and cooperating with it to limit thepivoting of the intermediate plateau relative to the tibial implant. 10.A prosthesis according to claim 1, characterized in that the femoralimplant and/or tibial implant comprise means for mounting on them one orseveral shims or spacers enabling compensation for possible boneablations or absences at the support surfaces of the implants againstthe femur and/or tibia.
 11. Series of components enabling composition ofthe prosthesis according to claim 1, characterized in that it comprises:a femoral implant, a tibial implant and an intermediate plateau; twointermediate coupling parts; two medullar anchoring rods assembled tothe aforementioned intermediate coupling parts.
 12. A series ofcomponents according to claim 11, characterized in that it comprisesshims or spacers for compensation of bone ablations or absences, havingdifferent thicknesses.
 13. A series of components according to claim 11wherein the femoral and tibial components of different sizes includeconnecting means for the medullar anchoring rods of identical dimensionsand shapes of one component to the other.
 14. A series of componentsaccording to claim 11 wherein more than two medullar anchoring rods,include different diameters, lengths, shapes.